The present invention concerns a process for preparing 8.alpha.-substituted 6.alpha.-methyl-10.alpha.-H-ergolines. Such compounds are either themselves biologically active, e.g., as inhibitors of endogen prolactin secretion and, therefore, as suppressants for nidation, in mammals, e.g., 3-(6-methyl-8.alpha.-ergolinyl)-1,1-diethylurea, or are intermediates for the production of other compounds which are biologically active, e.g., dironyl, sulergine and delergotrile having the above mentioned biological activity.
It is known that the trans-linked 10.alpha.-H-ergolines can be readily obtained from 8.beta.-substituted didehydroergolines by the catalytic hydrogenation of the 9,10-double bond. The situation, however, is different in the case of the 8.alpha.-substituted 9,10-didehydroergolines. Catalytic hydrogenation of 8.alpha.-substituted 9,10-didehydroergolines always results in mixtures consisting of the trans-linked 10.alpha.-H-ergolines and the cis-linked 10.beta.-H-ergolines. However, biologically active compounds are derived solely from the trans-linked ergolines, such as, for example, the conventional ergolines, dironyl, sulergine, and delergotrile.
Thus, in the catalytic hydrogenation of lisuride to dironyl with Raney nickel, depending upon the nature of the catalyst and the solvent, maximum yields of 66% of desired product are obtained (DOS [German Unexamined Laid-Open Application] No. 2,238,540), wherein the ratio of the desired 10.alpha.-H-isomer to the undesired 10.beta.-H-isomer is about 4:1.